The invention relates to a process for the manufacture of moulded articles that are partly coloured or have regions of different colours according to the preamble of the independent claim and to a moulded article manufactured by the process, having at least two regions, especially annular regions, of different colours. The invention relates specifically to the manufacture of optical moulded articles, especially contact lenses.
Coloured contact lenses are very common. In many cases, there is a need for the contact lenses not to be coloured over their entire area but to be coloured only in a central region while the peripheral region is to be substantially transparent.
For the manufacture of contact lenses of uniform colour throughout it is known to use an appropriately dyed monomer mixture from which the contact lenses are then manufactured in conventional manner, especially by the casting process. That casting process is described inter alia in U.S. Pat. No. 5,252,056. It is not possible in that manner, however, to manufacture contact lenses having partly coloured regions or regions of different colours.
Various processes are known for the manufacture of partly coloured contact lenses. According to one known process, disclosed, for example, in U.S. Pat. No. 4,553,975, a hydrated contact lens is masked at its periphery and immersed in a dyeing bath. The dyeing process typically lasts from 25 to 65 minutes and is carried out at temperatures of approximately 44.degree. C. Subsequently, the dye has to be fixed and the contact lens has to be extracted in a time-consuming manner. In another known process, described inter alia in U.S. Pat. No. 5,352,245, a dry contact lens manufactured by the casting process is printed with a stamp while it is still on the male half of the casting mould. After the printing operation, the dye has to be fixed and the contact lens has to be hydrated and extracted in a time-consuming manner. A feature common to both known processes, therefore, is that a (colourless) contact lens has to be manufactured first and then has to be dyed in further steps in a time-consuming manner.
By means of the invention a process of the generic kind is to be so improved that it does not require fixing of the dye and extraction of the moulded article and that consequently makes possible simpler and substantially faster manufacture of moulded articles, especially optical moulded articles and specifically contact lenses, that are partly coloured or have regions of different colours.
According to the invention, the process that solves that problem is one in which measured amounts of two or more crosslinkable materials of different colours are introduced into the casting mould in the uncrosslinked state unmixed, and, after closing of the casting mould, are crosslinked.
By means of those measures according to the invention the moulded article, specifically the contact lens, is given its coloration during its actual manufacture by the casting process and the laborious after-treatment that is otherwise customary becomes unnecessary. As a result, the process is especially fast and is particularly suitable for the rational mass production required, for example, in the case of so-called daily disposable contact lenses.
Other advantageous measures and preferred forms of the process will be apparent from the dependent claims. By means of those measures it is possible to influence the distribution of the differently coloured regions and the merging of the colours and the transitions between the colours in a controlled manner.